The invention relates to an arrangement for transporting metallic work pieces, especially during a heat treatment process, which is equipped with a heat-insulated transport chamber designed to hold the work pieces, means for loading and unloading the work pieces, and transporting gear for moving the transport chamber. The invention further relates to a system for heat treating metallic work pieces, which is equipped with at least two treatment chambers in which the work pieces may be heat treated. Furthermore, the invention involves a method for transporting metallic work pieces during a heat treatment process, in which the work pieces are transported within a heat-insulated transport chamber between at least two treatment chambers in which the work pieces may be heat-treated.
In order to generate specific properties for work pieces, such as a high degree of hardness or a high capacity of resistance to wear, metallic work pieces are usually subjected to a thermal or thermochemical heat treatment process. The heat treatment alters the microstructure of the work pieces, lending them the desired properties. In addition to the general processing parameters of pressure, temperature, and duration of treatment, the atmosphere in which the heat treatment is conducted is of particular importance to the outcome of the treatment. A number of processes are known in the art by which work pieces can be exposed to various atmospheres in order to obtain the desired treatment results. In such processes the work pieces are carried, one after another, to a plurality of treatment chambers in a heat treatment system. The individual treatment chambers are ordinarily connected to one another via a transfer canal, which serves to protect the work pieces during transport from environmental influences that could produce undesirable effects on the treatment results achieved up to that point. To this end, the transfer canal can be either filled with a protective atmosphere, such as is known, for example, from DE-A-43 16 841, or evacuated of air, such as is proposed in FR-A-2 771 754.
The disadvantage of transfer canals of this type is that the configuration of the course of the heat treatment system can be varied to only a limited extent. Further, dismantling such heat treatment systems is relatively costly, even in cases involving modular construction such as is known from FR-A-2 771 754. In terms of economy, it is also most unsatisfactory that maintenance work on individual treatment chambers, and especially on the conveyor car in the transport canal, necessarily requires the temporary shutdown of the entire heat treatment system.
Further, from U.S. Pat. No. 5,567,381 a heat-treatment system is known which is equipped with a vacuum furnace, a transfer canal, and a movable transport chamber. The transport chamber can be coupled to the vacuum furnace via the transfer canal. The transport chamber, which is heat-insulated from the outside and is equipped with a hermetically sealed door, is further equipped with a heating unit for heating the work pieces, and a lifting device for loading and unloading the work pieces. To transfer the work pieces, which have been heated to a certain temperature in the vacuum furnace, to a further treatment chamber, such as a quenching chamber, the transport chamber is coupled to the transfer canal and preheated. Both the transfer canal and the transport chamber are then flooded with an inert gas, until they reach a pressure that is greater than the ambient pressure, in order to prevent air from entering the transfer canal or the transport chamber from the outside. The work pieces in the vacuum furnace are then cooled to the temperature prevailing in the transport chamber, and the vacuum furnace is flooded with an inert gas. When the same pressure level has been reached in the vacuum furnace and in the transfer canal or transport chamber, the door of the vacuum furnace is opened, and the work pieces are loaded inside via the lifting device that is part of the transport chamber.
With the transport chamber described above, it is possible to transport heated work pieces from one treatment chamber to the next while exposing them to an atmosphere of inert gas, thus preventing an undesirable oxidation of the work pieces. Although the heat treatment system described in U.S. Pat. No. 5,567,381 offers a greater degree of flexibility than the heat treatment systems discussed above involving a stationary transfer canal, it carries with it the disadvantage that in coupling the transport chamber to the vacuum furnace, the transport chamber, the transfer canal, and the vacuum furnace are all flooded with the inert gas. Apart from the fact that providing the inert gas for such a system is highly costly, the inert gas also presents an obstacle to a continuous heat treatment process during transport of the work pieces from treatment chamber to treatment chamber. This is because the change in the atmosphere in the vacuum furnace triggered by the unavoidable flooding of the furnace with inert gas not only presupposes the conclusion of the heat treatment process in the vacuum furnace, but also is unavoidably connected with a cooling of the work pieces, due to the fact that the protective gas is not preheated. The latter is most disadvantageous for high-temperature heat treatment processes, in which, as a rule, no notable temperature fluctuations can be permitted.
The object of the invention is to provide an arrangement and a method for transporting metallic work pieces, and a system for heat treating these work pieces, which will enable a comparatively flexible and efficient transport of the work pieces among a plurality of treatment chambers during a heat treatment process.
This object is attained in accordance with the invention in an arrangement having the characteristic features described above, in that the transport chamber is designed to be vacuum-tight and can be evacuated of air to create a vacuum that will protect the work pieces from environmental influences.
An arrangement of this design, in comparison to the prior art stationary transfer canals, enables the flexible transport of the work pieces during a heat treatment process. For example, individual treatment chambers in a heat treatment system can be excluded from the process cycle to allow maintenance or repair work, without the other treatment chambers being involved. Further, with the arrangement specified in the invention, existing heat treatment systems can be expanded to include additional treatment chambers, without great expense.
Furthermore, this type of arrangement enables a considerably more efficient process due to the fact that, rather than flooding with inert gas, a vacuum is created in the transport chamber in order to protect the work pieces from undesirable environmental influences, such as oxidation caused by the introduction of oxygen. In contrast to the movable transport chamber specified in U.S. Pat. No. 5,567,381, with the arrangement specified in the invention it is possible to continue the heat treatment process inside the transport chamber during the transport of the work pieces from one treatment chamber to the next, without any noticeable change in temperature. In addition to the time that is saved with such an arrangement, providing an economic advantage, the arrangement is further characterized by its particular suitability for use with high-temperature heat treatment processes.
It is especially advantageous for the arrangement to be equipped with a vacuum pump for evacuating the air from the transport chamber. This offers the advantage that the arrangement is self-sufficient in terms of the evacuation of the transport chamber, and is thus not dependent upon the specific design of the treatment chambers. The transport chamber can thus dock, for example, with both vacuum furnaces and atmospheric furnaces, or with cooling chambers. Furthermore, providing the arrangement with a vacuum pump makes it possible for the transport chamber to be evacuated during the transport process. This comes to bear, for example, when, during the transfer of the work pieces from a treatment chamber into the transport chamber, the atmosphere prevailing in the treatment chamber is allowed to expand into the transport chamber in order to continue the heat treatment process in this atmosphere during the transport process, until shortly before it reaches the next treatment chamber.
It is further advantageous for the transport chamber to be heated. Although the heat insulation of the transport chamber already serves to counterbalance a drop in the temperature of the work pieces, which is generally sufficient over short transport distances, in cases of high-temperature heat treatment it may be necessary to use additional heat to hold the work pieces at the desired temperature. In this connection, it has proven highly expedient for the transport chamber to be provided with a removable thermal insulation, preferably made of steel. This type of insulation, made of chrome nickel steel, for example, can be easily removed to allow maintenance and repair work to be done. It offers the further advantage that, due to its low heat retention properties, the temperature of the transport chamber can be adjusted within only a few minutes, in other words it can be easily adjusted to the different temperatures of a number of treatment chambers.
In one particularly advantageous further development of the arrangement specified in the invention, the transport chamber is provided with a hermetically sealed loading door, which can be actuated via a drive mechanism, in order to ensure the self-sufficient docking of the transport chamber with a treatment chamber. Taking into account the disruptions that occur during regular operation, it can further be advantageous for the transport chamber to be provided with a hermetically sealable connecting door. By means of an external lifting device, for example, the transport chamber can then be unloaded through the connecting door, independent of the loading door, which under certain circumstances may not be freely accessible.
An extremely advantageous design for the arrangement specified in the invention is provided when the transport chamber and the transporting gear can be moved relative to one another. This arrangement makes it possible, in a simple manner, for the path of travel to be largely decoupled from the arrangement of the individual treatment chambers, making it dependent primarily upon the given operating conditions. In this connection, it has proven especially effective for the transport chamber to pivot horizontally, or to be arranged such that it can move in a straight line in a horizontal and/or vertical direction. The latter variation would be used, for example, in cases in which several treatment chambers are positioned vertically, one on top of another.
With respect to the effortless docking of the transport chamber to the treatment chambers, the loading ends of which may be oriented differently, it can be helpful, as an alternative or as a supplement to this, for the drive mechanism to be designed to enable a stationary rotation of the arrangement. In this case, for example, if the treatment chambers are positioned on both sides of a heat treatment path vis-a-vis their loading ends, it is sufficient for the transport chamber to be equipped with only one loading door, thus providing an economic advantage. The drive mechanism is preferably track-bound based upon operative requirements, or is freely controllable via induction loops embedded in the base. To achieve a comfortable loading of the work pieces from a treatment chamber into the transport chamber, or vice-versa, it has further proven advantageous for the device used to load and unload the work pieces to be equipped with a loading fork that can be moved horizontally and vertically.
To attain the above object involving a system for the heat treatment of metallic work pieces having the above-mentioned characterizing features, it is proposed that an arrangement in accordance with one of the claims 1 through 11 be coupled to the treatment chamber via a transfer canal from which the air can be evacuated.
A heat treatment system of this type capitalizes on the advantages offered by the above-described arrangement for transporting metallic work pieces. The inclusion of the transfer canal ensures that the work pieces can be transported between a treatment chamber and the transport chamber, protected from any environmental influences. The heat treatment system specified in the invention is characterized by a high degree of flexibility in terms of the transport of the work pieces between the individual treatment chambers, whereby a relatively high transfer rate and thus an economically efficient process can be achieved.
To ensure a highly compact and relatively lightweight design for the transport chamber, it is expedient to place the transfer canal on the treatment chamber, in a stationary position. Thus, each treatment chamber is provided with a transfer canal. In general, however, the transfer canal may also be designed as an integrated component of the transport chamber, or may be mobile. Although the latter embodiment is associated with higher construction costs, it makes sense to employ such a design when the heat treatment system is comprised of a large number of treatment chambers with long residence times for the work pieces, so that a mobile transfer canal can be used for a number of treatment chambers without problems with time constraints.
It is further expedient if the transfer canal can be evacuated of air, so that it can be operated independent of the treatment chamber being used, whether via a vacuum furnace or an atmospheric furnace. Further, with such a design it is possible for the transfer canal to be evacuated during the conveyance of the transport chamber to the corresponding treatment chamber, thus ensuring the most rapid process possible. Depending upon the specific application, however, it is also possible for the transfer canal to be evacuated via a vacuum pump that is part of the transport chamber. In one particularly advantageous embodiment of the system specified in the invention, the transfer canal is equipped with a drive mechanism for actuating the loading door of the transport chamber. This results in a particularly lightweight embodiment of the transport chamber, and thus relatively low costs for transporting the work pieces between the individual treatment chambers. With respect to the greatest possible variability in the design of the heat treatment system, the treatment chamber is expediently a vacuum furnace, an atmospheric furnace, or a cooling chamber.
In process terms, the above-mentioned object is attained with a method having the above-mentioned features, characterized in that the vacuum-tight transport chamber is evacuated to create a vacuum that will protect the work pieces from environmental influences, and the work pieces are transported within this vacuum from one treatment chamber to the next.
The transport of the work pieces within a transport chamber that has been evacuated to create a vacuum has proven most advantageous for the transport of work pieces that have been heated to a relatively high temperature, for example, 1,000xc2x0 C. In contrast to the current state-of-the-art in which work pieces are transported in an atmosphere of inert gas, this type of system serves to prevent a frequently undesirable drop in temperature. In a further development of the method specified in the invention it is further proposed that the transport chamber be coupled to the given treatment chamber via a transfer canal, to capitalize on the advantages described above. Finally, it is proposed that the transfer canal be evacuated separately, in order to ensure a continuous coupling of the transport chamber.